The Obama administration is increasingly concerned about the risks that rising violence in northern Mexico, prompted by drug gangs fighting over lucrative trade routes, could spill over into U.S.

• 奥巴马政府越来越担心墨西哥北部的暴力行为增多可能带来的风险，贩毒团伙为争夺利润丰厚的贸易路线的斗争可能会蔓延到美国。